See Figures 1, 2 and 3
Many 1975 and later Volvos models are equipped with an air injection reactor system. The system injects filtered air into the exhaust manifold in order to reduce emissions of carbon monoxide and hydrocarbons. The oxygen in the air reacts with the exhaust gas and promotes further combustion in the exhaust manifold.
The system consists of an air pump (belt-driven), a diverter valve, an anti-backfiring valve, and a separate air manifold which is attached to the exhaust manifold. Under normal conditions, air is pumped from the air pump via the diverter valve, the backfire valve and the air manifold into the exhaust manifold ports.
The air pump takes in filtered air which is then compressed and discharged to the diverter valve. The diverter valve sends the air through the backfire valve, except during deceleration. The diverter valve also releases some of the air into the atmosphere if the pressure from the pump is too great. The anti-backfire valve is one-way valve which prevents the exhaust gases from flowing back towards the air injection components, but allows the pump air to pass into the air manifold and exhaust manifold.
See Figures 4 and 5
Service the AIR system every 15,000 miles (24,155 km). Make sure the drive belt is in good condition on the air pump. If the belt breaks, the backfire valve must be checked. Make sure all attaching nuts and bolts for the air pump and bracket are secure.
To check the air pump, start the engine and listen for excessive noise from the pump. Remember that the air pump is not completely quiet in normal operation, and it can make a bit of a racket when it's cold. Normally, the noise rises in pitch as engine speed increases. Do not attempt to lubricate or repair the pump: it must be replaced.To check the backfire valve:
- Disconnect the hose from the diverter valve.
- Apply a vacuum to the hose: no air should come through. If it does, replace the backfire valve.
- Disconnect and plug the hose from the diverter valve.
- Run the engine at idle. Air should only be coming out of point A in the illustration.
- Increase the engine speed to 3000-3500 rpm, then quickly release the throttle. Air should now flow from points B in the illustration. If not, replace the diverter valve.